i cannot open my Apps to change credit card

What happens when you tap on your id in Settings > iTunes & App Store ? If it's greyed out then have you currently got Settings > General > Restrictions > Accounts (under the 'Allow Changes' heading) set to 'Don't Allow Changes' ?

Change Payment Information

Settings>iTunes and App Stores>Apple ID>View Apple ID>Sign-in>Payment Information

Hi
I have similar but a bit different problem. Would very much appreciate if you guys can help me to fix it.
1. I was using old (1st) Apple ID with loading different apps.
2. Later on I have changed it with the new (2nd) Apple ID
But!
When I try to get updates of the previously downloaded apps (which I have got with my 1st Apple ID) it shows in the password entering window my 1st Apple Id email!
Bug:
I am not able to doanloads the updates for the apps which has been received with the old Apple ID.

Note: all the possible measures like changing the id in settings of itunes, appstore, entering serial number with my new id have been already taken.

Please advice me what shall I do to remove my old Apple ID login (email) from all the possible windows while trying to get updates.
Thanks.

All apps, and any other content from the store, are tied to the account that downloaded them. If you created a new account, as opposed to updating your existing account with a new email address, then to be able to download updates to those apps with your new account you will have to delete them from your iPad (which will also delete their content/settings) and buy/download them with your new account

Thank you very much for your fast reply!
Now I will stop torture my ipad with different tricks trying to fix this issue. 🙂

Thanks!